Step 1: Concept Overview:
The question concerns identifying the scientist who discovered bacterial transformation. Transformation is the genetic alteration of a cell due to the uptake and incorporation of external genetic material from its environment.
Step 2: Detailed Explanation:
F. Griffith (1928): Experimented with virulent (S) and non-virulent (R) strains of {Streptococcus pneumoniae}. He found that mice injected with heat-killed S-strain bacteria mixed with live R-strain bacteria died, and live S-strain bacteria were isolated from them. He concluded that a "transforming principle" from the heat-killed S-strain transformed the live R-strain into the virulent S-strain, thus discovering bacterial transformation.
Lederberg and Tatum (1946): Discovered bacterial conjugation, a genetic transfer process between bacterial cells via direct contact.
Avery, McCarty, and Macleod (1944): Identified the "transforming principle" as DNA through experiments using enzymes to degrade different molecule types (proteins, RNA, DNA). They proved DNA's role in transformation.
Therefore, while Avery, McCarty, and Macleod identified the molecule responsible, F. Griffith discovered the phenomenon of transformation.
Step 3: Conclusion:
Frederick Griffith is credited with the discovery of bacterial transformation based on the historical sequence of these findings.